It really depends on what the supply looks like. They were batch released for a bit in 2021 and then went quiet again until a batch came out around Dec 2023. Since then, its been kind of quiet on the Shadow Birkin in favor of the Shadow Birkin Clutch which is currently plentiful. Letting your SA know you are interested is the first step, but yes, I would guess it would be a multiyear wait simply because you'll be waiting for another batch release from Paris and who knows when/if that will happen.